Can bottom trawling disturbance increase food production for a commercial fish species?

Fishery closures and marine protected areas are increasingly being used as tools to achieve sustainable fisheries. The "plaice box", a gear restriction area in the North Sea that was established to reduce the bycatch of undersized plaice (Pleuronectes platessa), is considered ineffective because there has been a shift in the distribution of juvenile plaice to the waters that remained open to bottom trawlers. Here we examine the hypothesis that bottom trawling benefits the small benthic invertebrates that form the food source for plaice and that the plaice box had a negative impact on food production for plaice. A size-based model of benthic communities indicates that the production of prey was low without trawling and maximal in areas that are trawled once to twice a year. Therefore, bottom disturbance may improve the feeding conditions for species that feed on small invertebrates. As plaice aggregate at the locations with the highest benthic biomass, this may explain the observed redistribution to areas outside the plaice box. We conclude that the plaice box may not have been the most appropriate measure to protect plaice from discarding and that the species' ecology should be considered when choosing the most appropriate management measure to achieve an objective.